1. Field of the Invention
The present invention relates to Fe—Cr—Al type alloys used for electric resistance wires, more particularly, to Fe—Cr—Ar type alloys with additions to improve workability thereof.
2. Description of the Related Art
In a conventional manufacturing method for Fe—Cr type resistance wires, Cr for stabilizing ferrite is added more than 14 wt % to improve oxidation resistance at high temperature as well as to obtain high resistivity and low coefficient of thermal expansion, and then Al is added to the Fe—Cr to form Al2O3 thin-film layer to improve heat resistance and corrosion resistance.
Because Al element reduces fluidity and workability it is added by only about 5.0 wt %. In addition, Zr, Ti, Mn, Nb, or rare earth elements are also added to increase adherence between matrix and the oxide layer and to form stable compounds in the matrix at high temperature. Therefore, recrystallization at high temperature is suppressed, which will result in superior workability at high temperature and better heat resistance.
Be is also an important element which can improve workability. Conventionally, Be is added less than 0.001 wt % to strengthen intergranular structure of a steel and to make grain finer. According to the addition of Be, it is possible to fabricate Fe—Cr—Al type alloys for electric resistance wires with improved workability.
Fe—Cr—Al type alloys for electric resistance wires of the best quality developed and manufactured at present has the strength of 70 Kgf/mm2 (for a 0.2 mm-diameter rod wire) and the highest operating temperature of 1400° C. Such Fe—Cr—Al type alloys for electric resistance wires, which are main material for high temperature electric furnaces, are used widely and variously in architecture and medical fields as well as in industrial fields such as material melting and heat treatments. The Fe—Cr—Al type alloys are also used as exhaust pipes of automobiles and structure materials applicable to special environment.
In these days, Ni—Cr type nichrome wires are mostly used as electric resistance wires in daily-life products whereas Fe—Cr—Al type ferritic alloys are used in industrial fields.
Ni—Cr type nichrome wires can not be used in industrial fields because they have relatively low operating temperature, about 1200° C., and, Fe—Cr—Al type ferritic alloys have restricted application fields despite the advantage of high operating temperature (above about 1400° C.) because of its poor workability.